JPH05234074A - Manufacture of magnetic disk and the magnetic disk - Google Patents

Abstract

PURPOSE:To provide a coating type magnetic disk which is less at the differences in reproducing outputs and the overwriting characteristics between the inner peripheral part and the outer peripheral part, compared to the conventional one, since a magnetic layer with a uniform film thickness or with a thinner thickness at the inner peripheral side and a thickness at the outer peripheral side can be formed. CONSTITUTION:When a coating film is formed on a rigid substrate 102 with a magnetic coating material 104 incorporating fine magnetic particles and a binder, and it is oriented and cured and then the magnetic disk is produced, magnetic fields are impressed at the time of forming the coating film, and the impressed magnetic field strength in the inner peripheral side of the substrate is made lager than the magnetic field strength in the outer peripheral side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a hard disk type magnetic disk and a magnetic disk.

[0002]

2. Description of the Related Art A hard disk type magnetic disk having a magnetic layer provided on a rigid substrate is used in a magnetic disk driving device used in a computer or the like. In recent years, these magnetic disks have a large capacity and a small size. Is making rapid progress.
These disks are usually manufactured by spin-coating a magnetic coating material, and then orienting and curing the magnetic coating material.

In the case of the coating type magnetic disk produced by the spin coating method as described above, the coating film becomes thin on the inner peripheral side and thicker on the outer peripheral side due to centrifugal force.

On the other hand, when performing magnetic recording on a magnetic disk,
Since recording and reproduction are performed at the same frequency, the recording wavelength in the inner peripheral portion is shorter than that in the outer peripheral portion due to the difference in relative speed between the inner peripheral portion and the outer peripheral portion of the disk and the magnetic head, resulting in high density recording. Therefore, even in the case of a magnetic disk in which the magnetic film has a uniform thickness, there arises a problem that the reproduction output is small at the inner peripheral portion and large at the outer peripheral portion.

Therefore, in the case of a disk having a thin inner peripheral portion and a thick outer peripheral portion such as the conventional coating type magnetic disk, the difference in reproduction output is further increased.

Further, the higher the relative speed, the larger the flying height of the flying magnetic head (distance between the head and the disk), and therefore the flying height increases toward the outer peripheral portion of the disk. Therefore, the overwrite characteristic becomes more disadvantageous toward the outer peripheral portion. Since the overwrite characteristic deteriorates as the film thickness increases, the conventional coating type magnetic disk having the recording layer thicker in the outer peripheral portion is further disadvantageous in terms of the overwrite characteristic in the outer peripheral portion.

As described above, the conventional coating type magnetic disk has a problem that there is a large difference in reproduction output and overwrite characteristics between the inner peripheral portion and the outer peripheral portion.

Then, from 14 inches, 8 inches, etc., 5
As the size of the magnetic disk advances to 3.5 inches, 3.5 inches, and 2.5 inches, the inner diameter becomes relatively large, and the ratio of the outer diameter to the inner diameter becomes large. The difference in centrifugal force at the peripheral portion becomes large, and the difference in coating film thickness becomes large. Further, since the ratio of the relative speed between the head and the disk at the time of recording / reproducing also becomes large, the difference between the reproduction output at the inner and outer peripheries and the overwrite characteristic becomes even larger.

As a method for solving such a problem, for example, Japanese Patent Publication No. 61-3545 discloses a coating method in which the viscosity of the coating material is controlled by the position of the coating material by spraying a gas, and then spin-out is performed. There is. By using this coating method, it is possible to increase the viscosity of the inner peripheral portion in advance to increase the film thickness on the inner peripheral side.
When the coating film thickness is 5 μm or less, it becomes difficult to control the film thickness, and the squareness ratio of the inner peripheral portion of the coating film decreases.

In order to solve such a problem, it is possible to form a thick magnetic layer once and then further polish the outer peripheral portion to reduce the film thickness of the outer peripheral portion. However, in this case, when the film thickness is 0.3 μm or less, the unevenness of the film thickness due to polishing, polishing scratches, and the like increase modulation at the time of recording / reproducing, resulting in frequent errors. ..

[0011]

The main object of the present invention is to provide a uniform film thickness at the inner and outer circumferences, or more preferably, at the inner and outer circumferences. It is to provide a method of manufacturing a magnetic disk having a thin magnetic layer, and a magnetic disk.

[0012]

The above objects are achieved by the present invention described in (1) to (4) below. (1) In a method for producing a magnetic disk, in which a coating film is formed on a rigid substrate with a magnetic coating material containing magnetic fine particles and a binder, and oriented and cured, a magnetic field is applied at the time of forming the coating film, the rigid substrate A method of manufacturing a magnetic disk in which the applied magnetic field strength on the inner circumference side is larger than the magnetic field strength on the outer circumference side.

(2) The method of manufacturing a magnetic disk according to the above (1), wherein polishing is performed after the curing.

(3) The method for manufacturing a magnetic disk according to the above (1) or (2), wherein the magnetic layer of the magnetic disk is thicker on the inner peripheral side than on the outer peripheral side.

(4) A magnetic disk having a magnetic layer on a rigid substrate, the inner thickness of this magnetic layer being thicker than the outer thickness.

[0016]

In the method of manufacturing a magnetic disk according to the present invention, a magnetic field is applied while the disk is rotated to apply a magnetic coating material to form a coating film. At this time, by applying a magnetic field in which the magnetic field strength at the inner peripheral portion of the disk is larger than that at the outer peripheral portion, a magnetic force in the inner peripheral direction is applied to the coating film to move the magnetic paint in the inner peripheral direction. As a result, a magnetic layer having a thick inner peripheral portion and a thin outer peripheral portion can be formed.

Such a magnetic disk has a small difference in reproduction output and overwrite characteristics between the inner peripheral portion and the outer peripheral portion.

Further, since a magnetic coating film having excellent surface smoothness can be formed by an applied magnetic field and the magnetic coating material can be prevented from drying until just before orientation, magnetic fine particles can be sufficiently oriented and a high squareness ratio can be obtained. For this reason, it is possible to obtain a magnetic disk with few errors and capable of lowering the flying height of the magnetic head.

[0019]

[Specific Structure] The specific structure of the present invention will be described in detail below. FIG. 1 shows a preferred example of the magnetic disk of the present invention.

In FIG. 1, a magnetic disk 101 has a coating type magnetic layer 103 on a rigid substrate 102. The present invention may be a single-sided recording type magnetic disk having the magnetic layer 103 on only one side of the rigid substrate 102 or a double-sided recording type magnetic disk having the magnetic layers 103 on both sides of the rigid substrate 102.

The disc-shaped rigid substrate 102 used in the present invention may be made of various non-magnetic materials such as metals such as aluminum and aluminum alloy, glass, ceramics and engineering plastics.
Among these, it is preferable to use aluminum, aluminum alloy, or the like, which has good mechanical rigidity and workability. The size of the rigid substrate may be selected according to the purpose,
Normally, the thickness is about 0.5 to 1.9 mm and the diameter is 40 to 130 mm.
It is a degree. The Rmax of the substrate is 0.005-0.0.
It is about 70 μm.

The magnetic layer 103 is formed by applying a magnetic coating material containing magnetic fine particles. The magnetic fine particles used in the magnetic layer are not particularly limited, and various oxide magnetic powders can be used, but ferromagnetic metal fine particles or hexagonal oxide fine particles are preferable. If ferromagnetic metal particles or hexagonal oxide particles are used, high recording density and high recording / reproducing sensitivity can be obtained. The ferromagnetic metal fine particles and hexagonal oxide fine particles to be used are not particularly limited, but it is preferable to select them so as to obtain the above magnetic properties.

The ferromagnetic metal fine particles include Fe, Co,
Ni simple substance, alloys thereof, or Cr, Mn, Co, Ni, and further Zn, C in addition to these simple substances and alloys.
Ferromagnetic metal fine particles to which u, Zr, Al, Ti, Bi, Ag, Pt, etc. are added can be used. Further, a small amount of a non-metal element such as B, C, Si, P or N may be added to these metals, or a partially nitrided material such as Fe ₄ N may be used.

Further, the ferromagnetic metal fine particles may have an oxide film on the surface in order to improve the corrosion resistance and weather resistance. As such oxides, oxides of metals forming ferromagnetic metal fine particles and various ceramics such as Al ₂ O ₃ are preferable.

The shape of the ferromagnetic fine particles is not particularly limited,
It is preferable to use a needle-shaped one because the shape magnetic anisotropy can be utilized. Further, the size of the ferromagnetic metal fine particles may be selected according to the intended structure of the magnetic layer,
Usually, the major axis is about 0.15 to 0.30 μm and the needle ratio is about 6 to 1.
It is preferable to use one of about 0. When the ferromagnetic metal fine particles are used, they may be produced by various known methods such as a method of reducing α-FeOOH (Goethite), or commercially available ones may be used.

The hexagonal oxide fine particles include magnetic fine particles such as barium ferrite and strontium ferrite. In this case, the size of the hexagonal oxide fine particles may be selected according to the intended constitution of the magnetic layer, but the average particle size is 0.15 μm or less, especially 0.0
2 to 0.10 μm, plate ratio is 2 or more, especially 3 to 10
Those having a degree are preferable. Here, the average particle is, for example, about 50 hexagonal barium ferrite particles observed by an electron micrograph, and the measured values of the particle size are averaged. The plate ratio is the value of average particle diameter / average thickness.

As barium ferrite, BaFe ₁₂
Hexagonal barium ferrite such as O ₁₉ or part of barium ferrite is Ca, Sr, Pb, Co, Ni, Ti, C
r, Zn, In, Mn, Cu, Ge, Nb, Zr, Sn
Examples include those substituted with one or more selected from other metals. As the strontium ferrite, hexagonal strontium ferrite SrFe
_It may be ₁₂ O ₁₉ or one obtained by substituting it according to the above. In this case, the surface of hexagonal ferrite may be modified with spinel ferrite in order to increase the amount of magnetization and improve temperature characteristics. Furthermore, in order to improve weather resistance and dispersibility, the surface of these particles may be coated with an oxide or an organic compound.

Examples of the method for producing barium ferrite and the like include a ceramic method, a coprecipitation-firing method, a hydrothermal synthesis method, a flux method, a glass crystallization method, an alkoxide method, a plasma jet method and the like, and any method is used in the present invention. You may use.

The magnetic coating material used for forming the magnetic layer is prepared by kneading the above-mentioned magnetic fine particles, a binder and a solvent.
The binder used is not particularly limited and may be selected from thermosetting resins, reactive resins, radiation curable resins, etc. according to the purpose, but it is necessary to secure sufficient film strength with a thin layer and obtain high durability. Therefore, it is preferable to use a thermosetting resin or a radiation curable resin.

Examples of the thermosetting resin include phenol resin, epoxy resin, vinyl copolymer resin, polyurethane curable resin, urea resin, butyral resin, formal resin, melamine resin, alkyd resin, silicone resin and acrylic reaction. Resin, polyamide resin, epoxy-
Polyamide resin, saturated polyester resin, polycondensation resin such as urea formaldehyde resin or a mixture of high molecular weight polyester resin and isocyanate prepolymer, a mixture of methacrylate copolymer and diisocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, Mixtures of the above-mentioned polycondensation resin and a crosslinking agent such as an isocyanate compound, such as a mixture of low molecular weight glycol / high molecular weight diol / triphenylmethane triisocyanate, a mixture of a vinyl copolymer resin and a crosslinking agent, nitrocellulose, cellulose A mixture of a fibrin-based resin such as acetobutyrate and a crosslinking agent, butadiene-
A mixture of a synthetic rubber system such as acrylonitrile and a crosslinking agent,
Furthermore, mixtures of these are preferred.

Particularly, a mixture of an epoxy resin and a phenol resin, a mixture of an epoxy resin described in US Pat. No. 3,058,844, a polyvinyl methyl ether and a methylol phenol ether, and JP-A-49-
A mixture of the bisphenol A type epoxy resin described in 131101 and an acrylic acid ester or methacrylic acid ester polymer is preferable.

Specific examples of the radiation curable compound include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds showing an unsaturated double bond having radical polymerizability, and diallyl phthalate. It is a resin in which a group of an allyl double bond, an unsaturated bond such as a maleic acid or a maleic acid derivative, which is crosslinked or polymerized by irradiation with radiation, is introduced or introduced into the molecule of the thermoplastic resin. In addition, any compound having an unsaturated double bond that undergoes cross-linking polymerization upon irradiation with radiation can be used.

The resin used as the radiation-curable binder is a saturated or unsaturated polyester resin containing the above unsaturated double bond in the resin molecular chain, at the terminal or in the side chain,
Polyurethane resin, vinyl chloride resin, polyvinyl alcohol resin, polyvinyl butyral resin, epoxy resin, phenoxy resin, fibrin resin, acrylonitrile-butadiene copolymer, polybutadiene and the like are preferable.

Further, the radiation-curable compounds used in the present invention as oligomers and monomers include monofunctional or polyfunctional triazine acrylates, polyhydric alcohol acrylates, pentaerythritol acrylates, ester acrylates, urethane acrylates and A monofunctional or polyfunctional methacrylate compound of the above system is suitable.

The content of the binder in the magnetic paint is not particularly limited, but it is 10 to 50 per 100 parts by weight of the magnetic fine particles.
It is preferable that the amount is about parts by weight.

The solvent used is not particularly limited, and various solvents such as a ketone system such as cyclohexanone and isophorone, an alcohol system such as isopropyl alcohol and butyl alcohol, a cellosolve system such as ethyl cellosolve and a cellosolve acetate, and an aromatic system such as toluene. It may be selected according to the purpose.

The content of the solvent in the magnetic coating material is not particularly limited, but is 400 to 700 with respect to 100 parts by weight of the magnetic fine particles.
It is preferable that the amount is about parts by weight. If desired, an abrasive such as α-Al ₂ O ₃ or the like, a lubricant such as silicone oil, or other various additives may be added to the magnetic paint.

Such a magnetic paint is applied to the surface of a rigid substrate whose surface is smoothed by polishing. In this case, the surface of the rigid substrate may be treated with an anodic oxide film such as alumite, an oxide film such as chromic acid, an electroless plating film such as Ni-P-Cu, a coupling agent, and a curable resin. ..

The method of applying the magnetic paint is not particularly limited,
The spin coating method is preferably used because uniform coating can be easily performed and the effect of the present invention can be effectively realized. By this spin coating, a stronger magnetic field is applied to the inner circumference side while the substrate is rotated while forming a coating film with the magnetic paint. By this magnetic field, a magnetic force acts on the coating film in the inner peripheral direction, and the coating film moves to the inner peripheral side.

In the present invention, the magnetic field applying device used is not particularly limited, but a preferred example is shown in FIG. 2 and will be described below with reference to the illustrated example.

A magnetic field is applied to the substrate 102 coated with the magnetic paint. The direction of the applied magnetic field is usually perpendicular to the substrate 102, but it may have some inclination.

The magnetic field strength at this time is 100 to 3000 G, especially 200 to 300 G in the innermost magnetic coating 104.
It is preferably 3000 G. If the strength is too low, sufficient force to move the coating film is not generated, and the leveling effect becomes insufficient. If it is too large, the surface properties of the coating film deteriorate.

In this case, the strength of the applied magnetic field depends on the substrate 102.
It is the largest in the magnetic coating material in the innermost diameter part, and increases continuously or stepwise from the outer diameter part to the inner diameter part. In order to apply such a magnetic field, a pair of rod-shaped magnets 203 and 204 magnetized to the main surface are used as shown in the figure,
These electrodes are arranged with the different poles facing each other with the substrate 102 sandwiched therebetween.

In order to make the magnetic field strength on the inner circumference side stronger than that on the outer circumference side, as shown in FIG. 2, a pair of magnets 202 and 203 having a uniform magnetic flux are used, and a facing gap is sandwiched on the inner circumference side. As described above, the pair of magnets 203 and 204 may be brought close to each other to increase the amount of magnetization on the inner peripheral side. Alternatively, for example, segment magnets having different magnetic field strengths may be connected to form rod-shaped magnets, and the magnets may be arranged in parallel at equal intervals to increase the amount of magnetization on the inner peripheral side. In addition, the magnetic flux can be adjusted by disposing a soft magnetic material on the surface of the magnet. Furthermore, these may be used in combination.

The magnet used may be a permanent magnet or an electromagnet, and the maximum energy product (BH) max and size of the magnet used depend on the size of the substrate, the applied magnetic field strength, the distance between the substrate and the magnet, etc. It may be selected appropriately. Normally, the (B
H) max is about 16 to 30 MGOe, and the distance between the magnet and the substrate is 5
Approximately 20 mm, and the size of the magnetic pole is approximately 10 × 65 mm. The value obtained by dividing the magnetic field strength on the outer peripheral side by the magnetic field strength on the inner peripheral side is 1.1 or more, preferably 1.5 or more, and more preferably 2 or more. The magnetic field strength may be zero at the outermost circumference.

The opposing magnets 203 and 204 are 1
Not only pairs, but 2 to 6 pairs may be provided. The magnetic field applying method is not limited to the above method,
Various methods are possible, for example, by arranging magnetic poles only on one side of the substrate and applying a vertical magnetic field.

A magnetic coating film having excellent surface smoothness can be formed by such an applied magnetic field, and moreover, the magnetic coating material can be prevented from drying until just before orientation, so that the magnetic fine particles can be sufficiently oriented and a high squareness ratio can be obtained. ..

Basically, the coating film is formed by coating at a relatively low rotational speed (2000 rpm or less, particularly 200 to 2000 rp).
About 1 second to 1 minute at m), shake off at high rotation speed (1
000 rpm or more, particularly about 1000 to 10000 rpm for about 1 second to 3 minutes), and then an alignment treatment is performed.
At that time, after forming the coating film and before orienting, if necessary, a low rotation speed (1 to about 200 to 3000 rpm for smoothing the coating film).
You may introduce the leveling process etc. of a second-5 minutes).
In forming the coating film, the applied magnetic field does not have to be constant during the formation of the coating film, and may be performed only in a part of the coating film formation, or the magnetic field distribution may be changed during the formation. In the leveling step, it is preferable to continue the application of the magnetic field to reduce the influence of the centrifugal force, but in some cases, a uniform magnetic field may be applied or it may be performed without a magnetic field.

In the present invention, it is also possible to apply a magnetic field to the coating film during coating film formation or leveling in an atmosphere in which solvent vapor is dissolved in air. The solvent used is not particularly limited as long as it is a solvent that can be used when preparing the magnetic coating material, and any solvent may be used, or two or more kinds may be used. In this case, the temperature of the atmosphere is 20-5
It may be 0 ° C. By doing so, the magnetic coating film can be prevented from drying until just before the orientation, so that the magnetic fine particles can be oriented sufficiently and a magnetic layer having a high coercive force squareness ratio S can be formed.

After applying a magnetic paint, forming a coating film and leveling, the magnetic fine particles are oriented. The magnetic paint is preferably oriented so that its easy axis of magnetization is oriented in the disk circumferential direction. In order to perform such an orientation, it is preferable to provide a pair of magnets so that the same poles face each other with the magnetic layer sandwiched therebetween, and rotate the magnetic disk with these magnets.

The magnetic field of the orienting magnet is 1000 to 1000 in the coating film.
About 10000G may be provided, and about 1 to 6 pairs of oriented magnets may be provided. At this time, the rotation speed is about 100 to 500 rpm, and the time is about 10 seconds to 10 minutes. A solvent vapor may or may not be present in the orientation atmosphere.

After orientation, the coating material is dried, if necessary, and then a curing treatment is performed to cure the magnetic coating material. When performing drying, the temperature is set to about 100 ° C. or lower.

When the binder is a thermosetting resin, various conditions such as heat treatment temperature and heat treatment time may be appropriately set according to the kind of the binder, but it is usually about 150 to 300 ° C. and about 1 to 5 hours. .. Further, in the case of a radiation curable resin, the dose may be set to 3 to 10 Mrad at room temperature. The atmosphere during the curing treatment is preferably an inert gas atmosphere, particularly a nitrogen atmosphere. In this way
It is possible to form a magnetic layer having a thin film thickness, a uniform thickness, and a small surface roughness. For example, the thickness of the magnetic layer after curing the magnetic coating film is preferably 0.6 μm or less, and particularly preferably 0.3 μm or less. In this case, it is preferable to make the inner peripheral portion thicker than the outer peripheral portion in terms of reproduction output and overwrite characteristics. The film thickness difference between the outer peripheral portion and the inner peripheral portion is preferably 40% or less. The surface roughness may be such that Rmax is 0.1 μm or less. As a result, the polishing process is shortened, and mass productivity and productivity are further improved.

After the magnetic paint is cured, it is preferable to polish the surface of the magnetic layer. Polishing may be performed with various abrasives such as an abrasive tape. By this polishing, the surface roughness of the magnetic layer can be set to a desired value, and the thickness of the magnetic layer can be adjusted as a matter of course. In the present invention, after curing, Rma
Since x can be reduced as described above, the Rmax of the magnetic layer formed by polishing is about 0.1 μm or less, especially 0.02.
The thickness can be less than 1 μm and at least about 1 nm.

After polishing the magnetic layer, it is preferable to apply a liquid lubricant to the surface of the magnetic layer to impregnate the magnetic layer. Although the liquid lubricant used is not particularly limited, it is preferable to use a liquid lubricant containing an organic compound containing fluorine because it has good lubricity. There is no limitation on the method of applying the liquid lubricant, and for example, a dipping method, a spin coating method or the like may be used.

It is preferable to further improve the smoothness of the surface of the magnetic disk by performing burnishing after impregnation with the liquid lubricant. Note that such a liquid lubricant may be contained in the magnetic paint.

[0057]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention. Example 1 A magnetic paint was prepared as follows. Magnetic powder 100 parts by weight Composition: α-Fe Coercive force: 1190 Major axis: 0.25 μm Needle ratio: 8 α-Al ₂ O ₃ 10 parts by weight Epoxy resin 28 parts by weight (Epicoat 1004, Shell Chemical Co.) Phenolic resin 12 Parts by weight (Sumirac PC25, manufactured by Sumitomo Bakelite Co., Ltd.) Silicone oil 0.4 parts by weight Cyclohexanone / isophorone (1/1 mixed solvent) 5
70 parts by weight The above composition was mixed and dispersed in a ball mill for 140 hours. The viscosity of the paint was 660 cps.

Next, in an atmosphere in which cyclohexanone vapor was present in the air, the disc was rotated by using a leveling device having slanted rod-shaped NS facing magnets shown in FIG. 2 at room temperature of 23 ° C. Coating film formation and magnetic field treatment were performed.

The coating film was formed by coating the obtained magnetic paint on both sides of a 3.5-inch disk-shaped aluminum substrate at a rotation speed of 4
Shake off at 000 rpm for 5 seconds, then rotate at 10
The leveling treatment was performed at 00 rpm for 20 seconds. The magnetic field was applied through formation of a coating film and leveling. The magnetic field strength in the coating film is as shown in Table 1.

Next, after an orienting treatment was carried out in the disk circumferential direction by an orienting device having opposed magnets, the paint was dried. The orientation magnetic field was made uniform in the paint at 3000 G, the rotation speed was 200 rpm, and the orientation time was 45 seconds.

Next, after a curing treatment was carried out at 200 ° C. for 3 hours in a nitrogen stream, a polishing tape WA10 was prepared by a tape polishing device.
000 (manufactured by Nihon Micro Coating Co., Ltd.) was used to polish the polishing amount to about 0.01 μm to smooth the magnetic layer.

Next, the disc is washed and the concentration is 0.1%.
A fluorocarbon (KRITOX 143CZ: manufactured by DuPont) fluorocarbon solution was applied by a dip method and impregnated to prepare a magnetic disk sample No. 1. Rma of the magnetic layer surface
x was 10 nm.

Next, a comparative sample was prepared in the same manner as in the example except that the magnetic field treatment at the time of coating film formation and leveling was performed by the magnetic field applying device using magnets having different magnetic field strengths as shown in FIG. No. 2 was produced. The magnetic field strength in the coating film is as shown in Table 1.

Next, Comparative Sample No. 3 was prepared in the same manner as in Example except that the coating film formation and the magnetic field treatment during leveling were not performed.

At the coating film position in these magnetic field applying devices, the magnetic field strength and the coating film thickness in each sample No. 1 to 3,
The reproduction output and the overwrite were measured at the inner peripheral portion (25 mm from the disc center), the center (the same 32 mm) and the outer peripheral portion (the same 39 mm) of the disc. The results are shown in Table 1.

[0066]

[Table 1]

The thickness of the magnetic layer was determined from the level difference at that location using the stylus type surface roughness diameter (taly step) after the inner area of the magnetic layer was provided in advance on the disk to be measured. The reproduction output and overwrite characteristics were measured using a floating magnetic head and a magnetic disk certifier. The magnetic head used for the measurement was a monolithic MIG head with a gap length of 0.6 μm, and the flying height of the head during recording / reproduction was 0.14 μm. The reproduction output is the PP value when the recording frequency is 3.3 MHz. The disk rotation speed during measurement was 3600 rpm.

The overwrite characteristic (O / W) is
The 1F signal (1.65 MHz) was overwritten with the 2F signal (3.3 MHz) to evaluate the attenuation of the 1F signal, and this was measured with a spectrum analyzer (manufactured by Hewlett-Packard Co.). The effect of the present invention is clear from Table 1.

[0069]

According to the method of manufacturing a magnetic disk of the present invention, it is possible to form a magnetic layer having a uniform film thickness or a thick magnetic film on the inner peripheral side and a thin film on the outer peripheral side. For this reason, it becomes possible to provide a coated magnetic disk in which the difference in reproduction output and overwrite characteristics between the inner peripheral portion and the outer peripheral portion is smaller than in the conventional case.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a preferred example of a magnetic disk of the present invention.

FIG. 2 is a front view for explaining the method of manufacturing the magnetic disk of the present invention.

FIG. 3 is a front view showing a comparative method of the magnetic disk manufacturing method of the present invention.

[Explanation of symbols]

 101 magnetic disk 102 rigid substrate 103 magnetic layer 104 magnetic paint 201, 301 container 202, 203, 302, 303 magnet 204, 304 solvent 205, 305 rotating shaft

Claims (4)

[Claims] 1. A method for producing a magnetic disk, comprising forming a coating film on a rigid substrate with a magnetic coating material containing magnetic fine particles and a binder, and orienting and curing the coating film. A method of manufacturing a magnetic disk, wherein an applied magnetic field strength on an inner peripheral side of a rigid substrate is made larger than an outer peripheral side magnetic field strength. 2. The method for manufacturing a magnetic disk according to claim 1, wherein polishing is performed after the curing. 3. The method of manufacturing a magnetic disk according to claim 1, wherein the magnetic layer of the magnetic disk is thicker on the inner peripheral side than on the outer peripheral side. 4. A magnetic disk having a magnetic layer on a rigid substrate, the thickness of the inner side of the magnetic layer being thicker than the thickness of the outer side.